Clad composites and aluminous metal compositions for cladding

ABSTRACT

Composite articles having a core and cladding composed of heattreatable aluminum base alloys, in particular a core alloy containing zinc, magnesium and copper as the principal alloying elements, clad with an alloy containing about 4-5.5% zinc and about 1-1.6% magnesium; and improved cladding alloys of that type.

United States Patent Fritzlen *May 6, 1975 CLAD COMPOSITES AND ALUMINOUS[58] Field of Search 29/1975 METAL COMPOSITIONS FOR CLADDING [75]inventor: Thomas L. Fritzlen, Richmond, Va. [56] UNITE SZ ETEZS SZiENTSAssign: Rfiygmlds 3 3.290.129 12/1966 Nock o 29 1915 3,342,565 9/]967Mundaym. 29/1975 1 N i The portion of he term of this 3,400.450 9/l968Nock I l l l 29/]975 patent subsequent to Dec 24. 1985 3,418,090 l2/l968Fritzlen 29/1975 h b l d.

as een dlsc mme Primary Examiner-L. Dewayne Rutledge [22] Filed: Nov.16, 1973 Assistant ExaminerArthur J. Steiner Attorne A em or FirmGlennPalmer L ne & A N 6 4 8 i y [2|] ppl 0 41 ,69 Gibbs Related U.S.Application Data [60] Division ofSer. No. 148.368. June 1, I971. Pm. N0.ABSTRACT 3324-083 which is a continuation of F- Composite articleshaving a core and cladding com- -9' abandoned whch posed ofheat-treatable aluminum base alloys, in parg g g if? 8 3 F 2 ticular acore alloy containing zinc, magnesium and Z a copper as the principalalloying elements, clad with an alloy containing about 4-5.5% zinc andabout l-l.6% 52] U S 29,1975 magnesium; and improved cladding alloys ofthat type. [5 I] Int. Cl B32b 15/00 5 Claims, 4 Drawing Figures PATENTEUHAY 61975 SHEET 10F 2 LCNGTTUDINAL M086 CLAO 7072 CLAD I 0 T P I c 5 E DH E R C E P S D 6 Z I MIR IHUII STRESS RAXIHUM STRESS CYCLES T0 FAILUREFIG.

FLEXURAL FATIGUE 0F 0.063" 7079 ALLOY SHEET GLAD U l TH 7072 AND M086ALLOYS m E s m T M986 0 LAD Zil 3; one

"I! IMLIH STRESS MAX INUM STIE CYCLES T0 FAILURE FLEXURAL FATIGUE 0?0.083" 7079 ALLOY SHEET CLAD H TH 7072 AND M086 ALLOYS PF IIENIEU 55753,881 ,883

SIIEEI 20F 2 LONGITUDINAL /I.75' RADIUS 7072 GLAD N086 OLHJ W 35 n 175mlG SPECINEII DESCRIPTION 16 U7 I- 25 (II I D E X NIIINUM TRESS MAXIMUMSTRESS 1o Fl 6 3 CYCLES TO FAILURE 107 10 AX I AL TENSION FATIGUE OF0.063" 7079 ALLOY SHEET CLAD WITH 7072 AND M086 ALLOYS TRANSVERSE 7072GLAD DB6 CLAD MAX I MUM STRESS. I000 PSI Nlllllllll ETIZSS IAXIIIUISTIEQS 105 0 CYCLES TO FAILURE 107 M I M TENSION FATIGUE DF 0.063" 7079ALLOY SHEET CLAD II ITH 7072 AND M086 ALLOYS CLAD COMPOSITES ANDALL'MINOIS METAL COMPOSITIONS FOR (LADDING This application is adivision of Ser. No. 148.868 tiled June l. l97l (now US. Pat. No.3.824.083). which is a continuation of Ser. No. 838.0l 3 filed June 17.I969. which in turn is a continuation of Ser. No. (109.707 filed Dec.23. I966. both now abandoned. which is in turn a continuation-in-part ofSer. No. 538.085 (now l..'.S. Pat. No. 3.4l8.090) filed Mar. l4. Who.

The invention relates to aluminous metal cladding materials andcomposite articles; and. more particu larly. to a heabtreatable cladcomposite having a core composed of an aluminum base alloy containingzinc. magnesium and copper. and a cladding composed of a compositionallysimilar alloy containing little or no copper.

It is conventional in the art to employ cladding materials forprotecting base metals from corrosion. and for other purposes. Includedin this category are alclad products in which the cladding consistsessentially of aluminum or aluminum alloyed with a small percentage ofzinc. Various aluminum base alloys have been so clad. including 7000series alloys (Aluminum Association designation) which contain Zinc asthe principal alloy addition. as well as magnesium and copper in someinstances. in lesser amounts. lt is also known in the art to clad otherthan aluminum-zinc alloys with a cladding which contains both zinc andmagnesium alloyed with aluminum.

While the aluminum-zinc-magnesium-copper alloys exhibit relatively highmechanical properties. particularly after heat treatment. they aresusceptible in many instances to various types of corrosion. and it haslong been a problem facing the art to devise effective means of assuringprotection against corrosion. while maintaining the desirable strengthcharacteristics of composite articles having a core composed of such analloy. ()ne of the disadvantages of conventional cladding materials istheir dissimilarity to aluminum-zinc-magnesiuni-copper alloys inresponse to heat treatment. Pure aluminum and conventional claddingcomposed of aluminum alloyed only with zinc do not respond to solutionor precipitation heat treatment. A noteworthy advantage of the presentinvention is the provision of a composite metal article that is entirelyheattreatable. and in which the cladding and core alloys are responsiveto a common solution heat treatment and precipi tation hardeningpractice.

In accordance with the invention. a clad composite is provided whichincludes a cladding layer composed of an aluminumbase magnesiumcontaining about 4 to 5.55? zinc. about 1 to lb /r magnesium andsubstantially no copper. with a solution potential close to l volt. Thecore alloy may be any aluminum-zincmagnesiunvcoppcr alloy having anelectrode potential less clectro-negativc than the cladding. preferablyby at least about 0. l0 volts in order to assure adequate protection ofthe core. Suitable core alloys include 7001. X7002. 7075. 7079 and 7l78.Such alloys generally contain up to about 8'? vine. 4'; mangcsium and3"? copper. ordinarily with less copper than magnesium and lessmagnesium than IlllL.

A preferred cladding alloy is one which consists cssentially ol-l 1-4.8;7inc. l.0l.-$'; magnesium. about 0. l().30'1' manganese. about.05-.20'r' chromium. and not more than .05; copper. balancesubstantially aluminum. The cladding may contain up to about 020);silicon and 0.25% iron. typically introduced as incidental impurities inthe aluminum.

The combination of cladding and core alloys according to the inventionproduces the additional advantage of superior stress corrosionresistance compared to either the cladding alloy itself or a compositeof the same core alloy clad with an alloy of aluminum and a smallpercentage of line. A further improvement exhibited by such cladcomposites is a substantial increase in the endurance limit for fatiguepurposes as shown in the accompanying drawings. The results presented ingraphical form in the drawings are based on tests described in Exampleill.

The following examples are illustrative of the invention. but are not tobe regarded as limiting.

EXAMPLE I A l2 X 45 inch ingot was produced from an alumi- The ingot washomogenized 24 hours at 915--)-l0 F.. and hot rolled to 0.330 inchthickness. A scalped and homogenized ingot of 7079 alloy was clad withthe 0.330 inch stock of alloy A by slabbing to 3% inches. reheating toabout 840 F.. rolling to 0.125 inches. annealing. and cold rolling tofinal thickness. to produce .085-inch thick sheet having a nominal 2/47: cladding.

Additional specimens of alclad 7079 (having the same core compositionand a nominal 47: cladding of 7072 alloy) were provided for purposes ofcomparison.

The aforesaid clad products in heat treated (-Tb) condition were foundto have the following characteristics:

A. Solution Potentials (l-adding: 0.9-t volts Cladding: H198 \olts('ore: -0.85 volts .JOllensured against a 0 ll\ talomel electrode In LONNafl (I 3'; H4);- electrolyte B. Mechanical Properties C. StressCorrosion Specimens cut in the long transverse direction from each ofthe sheet materials were subjected to an alternate immersion test [0minutes each hour in 3 /2"? NaCl solution) under a constant load of 75";of the yield strength. and the results were as follows:

Exposed Stress Material Le\el (lv'siI lime to l'ailure Alclad (Al-l' iZn) 44.2 4 il l 7) days (lad (Alloy A) 50.0 No failures 7079-Th at 90days Alloy A-Tn 41s 5043 57 D. General Corrosion The material clad withalloy A also exhibited good corrosion resistance when totally immersedin Richmond tap water. when exposed for 96 hours in 5)? NaCl spray. andwhen exposed to the -hour CASS (CST.

EXAMPLE ll Following generally the procedure of Example I. additionalclad sheets were produced in thicknesses of .063 inch (nominal 29 27:cladding), 0.l inch (nomiand 250 F. for 24 hours. Flesural fatigue andaxial tension fatigue specimens were prepared from the thus heat-treated(-Tfi) materials. the configuration of the fatigue specimens being shownin FIGS. I and 3 of the 5 accompanying drawings. In the drawings. thedesignation M0811 is employed to denote the products having a claddinglayer in accordance with the invention.

Both longitudinal and transverse specimens were tested in each case.Prior to testing. the specimens were deburred and edges smoothed with600 grit emery paper.

The axial fatigue tests were done on an Amsler \ibrophore operated at afrequency of approximately l H) cycles per second.

The flesural fatigue tests were done on Krouse machines at a frequencyof 1.725 cycles per minute. with each specimen loaded as a cantileverbeam.

The results of the flexural fatigue tests are displayed graphically inthe drawings. where it can be seen (FIG. I) that the endurance limit at10.000000 cycles. with a minimum-to-maximum stress ratio ofminus one (Rl) was about lfi.000 psi (longitudinal) for the products of theinvention. compared to only about 8.000 psi for the conventionalmaterial under the same test con- 7 i nal Hi9? claddinghmd 0.188inchinominal lVf/r claddltions; and (FIG. 2) about l2.000 psi(transverse). ding). using the following aluminum alloy combinacomparedto somewhat less than 8,000 psi. tions containing the indicatedadditional elements: The corresponding axial fatigue data for l0.000.000

Others Cu Fe Si Mn Mg Zn (r Ti each total .06] Gauge ingot .64 .IS .ll.20 3.49 4117 .l5 .05 .05 max l).l5 ma\ Liner .112 .12 .06 .21) 1.244.43 .111 .03 do. do. (H25 (iauge lt'tgttl .h4 14 .(19 .l) 3.6] 4.h7 .ll05 do do Liner .02 .12 .0h .20 L24 4.43 .10 .03 do. do. (H88 (iaugelngot .69 .l4 .l0 .2l 3.39 4.57 .lo .05 do do. Liner .02 12 .06 .20 1.194.4: .11 113 do. do

Specimens of each have completed more than H7 days without stresscorrosion failure. under test conditions described in Example I. Resultswith respect to solution potential and mechanical properties are givenbelow:

A. Solution Potentials cycles (and R 0) were about 25.000 psi(longitudinal) and about 20.000 psi (transverse). compared to about15.000 psi (both longitudinal and transverse) for the conventionalmaterial. These data are shown graph g ically in FIGS. 3 and 4.

Cladding Core .003 Gauge l.0l volts -0.lt8 \olts (H25 ll )9 volts ().88volts 0188 l.0() volts 0.X7 volts B. Mechanical Properties T.S. (Ksi)Y.S. (Ks-i) Hongl'i) .063 (iau t- 79.4 671) 12.x 0125 80.0 l H 3 (LIXK79.8 68.] 120 EXAMPLE lll Additional samples from the same lot as the.063 gauge clad sheets of Example ll (having the same ingot and linercompositions). as vvcll as comparison sheets of conventional 7072-cladalloy 7079 also .063 inch thick. were heat treated at 8258-l0 F. forabout 7 M minutes. quenched in water F. ma\. and aged in two stepsconsecutively at about 200 l. for 8 hours said core alloy consistingessentially ol aluminum. (mil-8.0% zinc. Zia-3.4% magnesium, l.b-2.n/rcopper and dill-0.35% chromium.

2. An article comprising a clad composite having a core of aluminumalloy X7002. and a cladding composed of an alloy consisting essentiallyof aluminum. about 4-5.5'k zinc and about l-l.h/i magnesium. by weight;said core alloy consisting essentially of aluminum. 3.04.07: zinc.Ell-3.0% magnesium. (LSll-llll copper. .(lS-(LfllV/r manganese and(LID-0.309% chromium.

3. An article comprising a clad composite having a core of aluminumalloy 7075. and a cladding composed of an alloy consisting essentiallyof aluminum. about 4-5.5'7: zinc and about 1-! .67! magnesium. byweight; said core alloy consisting essentially of aluminum. 5.1-6.171zine. 21-25% magnesium. LIZ-2.0% copper lll and t). l 8-0.3.W chromium.

4. An article comprising a clad composite having a core of aluminumalloy 7079. and a cladding composed of an alloy consisting essentiallyof aluminum. about 4-5.5: zinc and about l-l.6/r magnesium. by weight:said core alloy consisting essentially of aluminum. 3.8-4.87? zinc.2.94.794 magnesium. 0.40-0.864 copper. 0.10-0.3071 manganese and(HO-0.25% chromium.

5. An article comprising a clad composite having a core of aluminumalloy 7 l 78. and a cladding composed of an alloy consisting essentiallyof aluminum. about 4-55: zinc and about 14.6% magnesium. by weight; saidcore alloy consisting essentially of aluminum. 6.3-7.3'7' zinc.2.4-3.171 magnesium. iii-2.4% copper and OAS-0.35% chromium.

1. AN ARTICLE COMPRISING A CLAD COMPOSITE HAVING A CORE OF ALUMINUMALLOY 7001, AND A CLADDING COMPOSED OF AN ALLOY CONSISTING ESSENTIALLYOF ALUMINUM, ABOUT 4-5.5% ZINC AND AOUT 1-1.6% MAGNESIUM, BY WEIGHT,SAID CORE ALLOY CONSISTING ESSENTIALLY OF ALUMINUM, 6.8-8.0% ZINC,2.6-3.4% MAGNESIUM, 2.6-2.6% COPPER AND 0.18-0.35% CHROMIUM.
 2. Anarticle comprising a clad composite having a core of aluminum alloyX7002, and a cladding composed of an alloy consisting essentially ofaluminum, about 4-5.5% zinc and about 1-1.6% magnesium, by weight; saidcore alloy consisting essentially of aluminum, 3.0-4.0% zinc, 2.0-3.0%magnesium, 0.50-1.0% copper, .05-0.30% manganese and 0.10-0.30%chromium.
 3. An article comprising a clad composite having a core ofaluminum alloy 7075, and a cladding composed of an alloy consistingessentially of aluminum, about 4-5.5% zinc and about 1-1.6% magnesium,by weight; said core alloy consisting essentially of aluminum, 5.1-6.1%zinc, 2.1-2.5% magnesium, 1.2-2.0% copper and 0.18-0.35% chromium.
 4. Anarticle comprising a clad composite having a core of aluminum alloy7079, and a cladding composed of an alloy consisting essentially ofaluminum, about 4-5.5% zinc and about 1-1.6% magnesium, by weight; saidcore alloy consisting essentially of aluminum, 3.8-4.8% zinc, 2.9-3.7%magnesium, 0.40-0.8% copper, 0.10-0.30% manganese and 0.10-0.25%chromium.
 5. An article comprising a clad composite having a core ofaluminum alloy 7178, and a cladding composed of an alloy consistingessentially of aluminum, about 4-5.5% zinc and about 1-1.6% magnesium,by weight; said core alloy consisting essentially of aluminum, 6.3-7.3%zinc, 2.4-3.1% magnesium, 1.6-2.4% copper and 0.18-0.35% chromium.